Piston construction for an aerosol container



May 12, 1964 H. T. HOFFMAN, JR., ETAL PISTON CONSTRUCTION FOR AN AEROSOL CONTAINER Filed Oct. 18. 1960 United States Patent O The present invention pertains to a movable wall member within a container adapted to dispense products therefrom by its movement. More particularly, it pertains to a cup-shaped, lfree piston adapted to dispense a viscous product disposed on one side thereof in a container upon its movement under the impetus of a pressure producing gas, also enclosed within the container and disposed on the opposite side of the piston.

The prior art discloses a -wide variety of pressure or aerosol-type containers for the packaging and dispensing of viscous products, such as toothpaste, mayonnaise, mustard, and the like. Insubstantially tall of these prior art containers, the product is separated from the gaseous propellant by means of a movable wall or piston. Upon actuation of the dispensing rvalve associated with these containers, the pressure generated by the gaseous propellant moves the piston longitudinally within the` container, forcing the viscous product through the dispensing orifice and out of the container.

Among the prime objectives of containers of this type is to utilize a piston which provides an effective seal between the product side and propellant side thereof and to insure substantially complete removal of product from the container. To obtain these objectives, pistons having various constructions and configurations have been designed. However, all of these prior art configurations rely in one way or another upon tight engagement between the outside surface of the piston and the inside surface of the container. Such a construction often leads to jamming of the piston within the container due to irregularities in the container wall, such as dents, or

due to excessive friction between 'the piston and the can wall.

It is therefore an object of the present invention to provide a piston for an `aerosol container which provides an effective seal between the product and propellant sides of the piston but at the same time provides a minimal frictional resistance to movement of the piston within lthe can body.

Another object is to provide a piston for a container of the character described which is relatively simple and inexpensive to manufacture.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which, taken in connection with the accompanying drawings, discloses a preferred embodiment thereof.

The above objects are accomplished Iby constructing a piston for use in an aerosol-type container, 'which piston has a substantially cylindrical but slightly tapered body, the maximum diameter thereof being slightly less than the interior diameter of the can with which it is to be utlized, an `arcuate wall integral with the smaller diameter end of the body curving appreciably inwardly to merge and be integral with la piston face.

Referring to the drawings:

FIGURE l is an elevational view `partly in section showing the piston of the present invention mounted within an aerosol-type container;

FIG. 2 is lan enlarged sectional View taken substantially along line 2 2 of FlG. l; and

FIG. 3 is a sectional view maken substantially along line 3--3 of FIG. 2.

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As a preferred or exemplary embodiment of the instant invention, FIG. 'l shows a metal can generally designated 10 having fa cylindrical body 111 with upper and lower ends 13, `14 respectively. The can 10 illustrated is of three-piece construction wherein the upper and lower ends 13, 14 are attached to the body E11 by means of conventional double seams 15, 16. 'It is to be understood, however, that the can 10l may be of two-piece construction wherein one end and the body are one piece, formed such as by drawing or impact extrusion, and the other end is secured to the body by an end seam. Mounted in lche upper end 13 is a conventional aerosol dispensing valve 17. Any construction well known in the lart may fbe used for the dispensing valve 17, such as that shown in U.S. Patent 2,615,597, :and further description thereof is deemed unnecessary. Enclosed within the upper portion of the body 11 and in contact with the inwardly extending portion of the dispensing valve 17 is a viscous product 18, such as toothpaste. Adjacent the lower end 14 and extending across the can body 11 is a piston 20 composed of a plastic such as polyethylene, preformed, such as by injection molding, prior to assembly with the can 10 into a cup shape that will be described more flully hereinafter. Beneath the piston 20 and separated from the product by the piston is a gaseous propellant 21, such as nitrogen gas. In the center of the end 14 is a hole 22 closed and sealed by a plug 23 composed of .rubber or some similar soft material. The gaseous propellant 21 is introduced into the container, after placement of the piston and Ifilling of the product, through the hole 22, either before the plug 23 is mounted therein or `after its mounting by means of a hypodermic needle inserted therethrough.

The gas 21 maintains the pressure within the container -substantially yabove atmospheric, usually about `100 lbs. per square inch. Actuation of the dispensing valve 517 unbalances the forces on either side of the piston whereby the piston moves upwardly due to l'the pressure of the gaseous propellant, thereby dispensing the product 18 until the valvey 17 is closed.

It is essential that a seal be maintained between the product side of the piston and 'the propellant side of the piston lat all times after the can is pressurized. If this condition is not met, leakage will occur around the piston, permitting the product and propellant to become intermingled. Obviously, such a condition is undesirable, otherwise the construction utilizing Ia piston or movable wall to separate the product )and propellant would be unnecessary.

We have found, contrary to the disclosures of the prior art, which teaches tight sealing contact between the movable wall or piston per se and the inner surface of the can, that a most efficient operation results from this container if the piston is purposely constructed to permit a thin layer of product to form between the outside surface of the piston and the inside surface of the can body.` This thin layer of `product forms not only a sealant or a gasket between the two members but also provides a lubricating layer, allowing smooth, low friction movement of the piston.

To this end, the piston 20 has a substantially cylindrical but slightly tapered body 25, the maximum diameter of which is slightly less than the internal diameter of the can with which it is to be utilized. The wall of the body 25 is relatively thin, from .017 inch to .025 inch, and preferably about .020 inch thick, and quite exible. The flexibility is essential, so that should there be irregularities in the side wall of the can body 11, such as a dent, the piston body wall may deflect inwardly around such irregularities without catching or jamming thereagainst. The relationship between the piston body 25 and the can wall 11 is shown in the dot-dash lines in FIG. 3, with the indentation 26 representing the type of irregularity discussed immediately above. It is to be understood that due to the inherent structural rigidity of the can and relatively high internal pressure within the can, large dents are highly unlikely to occur, so that the flexibility of the piston body 25 is more than adequate to compensate for small dents such as 26.

Integral with the smaller diameter end of the piston body 25 is an arcuate wall 27 which curves appreciably inwardly toward and is integral with a piston face generally designated 28. In the embodiment shown, the piston face 28 is composed of a horizontal wall 29 extending transversely of the piston body 25 and a sloping wall 3i) joining the horizontal wall 29 to the arcuate wall 27. The piston face 28 will be contoured to t relatively snugly over and around the portion of the valve 17 extending into the can 1t) so that the maximum amount of product will be dispensed from the can. Therefore, the particular shape of the piston face 28 may vary depending upon the particular shape of the valve 17.

The appreciable curvature of the arcuate wall 27 is an essential and critical element of the instant invention. Due to this curvature, product in contact therewith is conducted in a smooth, even ow into the small :space existing between the outside surface of the piston body 25 and the inside surface of the container, thereby facilitating the Vformation of a sealing-lubricating layer or iilm between the piston body and can body. The outward taper of the piston body wall 2S from its juncture with the arcuate Wall 27 toward its free end is desirable to leave as thin a film as possible of the product between the piston and the can body wall so as to dispense the maximum amount of product from the container. However, to repeat for ernphasis, the maximum diameter of the piston is slightly less than the internal diameter of the can body. With this construction, the piston does not scrape the can body wall clean, but leaves behind a thin iilm of product.

The arcuate wall 27 and piston face 28 are of substantially equal thickness and are substantially thicker and more rigid than the piston body 25. This greater rigidity, especially of the wall 27, is essential to minimize, if not prevent, deformation of the predetermined and critical shape of the wall 27 and face 28. Conditions tending Vto cause such deformation are the pressure of propellant gas, the weight of the product, vacuumizing or deaeration of the container immediately prior to pressurizing with propellant, or the heated state of the product if a hot-fill operation is used. The extra thickness and rigidity of the wall 27 enables it to resist such deformation. On the other hand, due to its appreciably curved surface, it can ride over any irregularities in the can body, such as the definitely preferred that the piston face 28 as Well as the arcuate wall 27 be of equal thickness and be substantially more rigid than the piston body 25.

On the interior surface of the piston body 25 is a plurality of longitudinally disposed, inwardly extending ribs 31. The container embodying the piston of the instant invention is mass produced by modern, high-speed production methods. To this end, the subject pistons are fed into an assembling machine from a hopper containing the pistons in a random bulk load. The ribs 31 prevent adjacent pistons in such a load from nesting or telescoping so that each piston may be readily released from the load and fed into the assembly machine. It is also believed that the ribs 31 provide some expansion resistance to the piston bady wall, while at the same time permitting ready exing of the piston body 25 from the top to the bottom thereof. The expansion resistance provided by the ribs 31 restricts ballooning of the piston body 25' at its inidpoint due to the internal pressure of the lgaseous propellant 2l. Such ballooning would tend to force the central and upper portion of the piston body 25 into intimate Contact with the can wall 11, thereby inhibiting the formation of the sealing-lubricating layer or film of product.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction, and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

We claim:

l. A free piston for acting on conned viscous uids, comprising an elongated tubular body having a thin, ilexible wall, and a rigid end wall integral with and closing one end of said body to form a unitary cup-shaped configuration therewith, said end wall being substantially thicker than said body and comprising a face `and a peripheral arcuate portion which merges with said flexible body wall in a substantially tangential juncture and extends radially inwardly therefrom with appreciable curvature toward the axis of said piston to deiine asmooth, continuous flow control surface.

2. The piston of claim l wherein said tubular body is tapered, said end wall closing the smaller diameter end thereof.

3. The piston of claim l wherein said body has a plurality of widely, circumferentially spaced ribs extendling longitudinally of its axis on its inner surface to the juncture with said arcuate portion.

4. The piston of claim 1 wherein said face includes a transversal, planar portion disposed radially inwardly of said arcuate portion.

5. The piston of claim 4 wherein said transversal and said arcuate portions are of substantially equal thickness.

References Cited in the file of this patent 

1. A FREE PISTON FOR ACTING ON CONFINED VISCOUS FLUIDS, COMPRISING AN ELONGATED TUBULAR BODY HAVING A THIN, FLEXIBLE WALL, AND A RIGID END WALL INTEGRAL WITH AND CLOSING ONE END OF SAID BODY TO FORM A UNITARY CUP-SHAPED CONFIGURATION THEREWITH, SAID END WALL BEING SUBSTANTIALLY THICKER THAN SAID BODY AND COMPRISING A FACE AND A PERIPHERAL ARCUATE PORTION WHICH MERGES WITH SAID FLEXIBLE BODY WALL IN A SUBSTANIALLY TANGENTIAL JUNCTURE AND EXTENDS RADIALLY INWARDLY THEREFROM WITH APPRECIABLE CURVATURE TOWARD THE AXIS OF SAID PISTON TO DEFINE A SMOOTH, CONTINUOUS FLOW CONTROL SURFACE. 